Creating a billion-dollar company isn't the only thing the founders of Reddit, Quora, Dropbox, Venmo, Airbnb, Instagram, Palantir, Pinterest, Lyft, Wish, Sofi, and Facebook have in common.

The 17 people who make up that list also happen to be men who were born within three years of each other, between 1981 and 1984.

The question of why, exactly, seven of the top 10 billion-dollar-plus unicorns, along with a handful of publicly traded titans, were all launched by guys who could have been in the same high school class doesn't come with just one answer. But there are clear events throughout history that offer clues.

Going back to the 1970s

The arc of the early-30s techie actually began in the 1970s, with the prior generation of computer programmers, according to technology consultant Tim Bajarin. "The Bill Gateses of the world were actually the precursor to this," Bajarin told Business Insider.

People like Gates and Steve Jobs began working in the 1970s, alongside lesser-known luminaries like Mitch Kapor of Lotus and Fred Gibbons of Software Publishing. They mostly worked on mainframes and mini-computers, and they spent thousands of hours doing so. When the first personal computer debuted in 1975, these small-time programmers were poised to strike it rich.

As Malcolm Gladwell noted of this tech generation in his book 2008 "Outliers," they came of age in a special time. If they were slightly older, they would have left college to work for a large corporation, like IBM, and their career would have been set in stone. On the other hand, if they were born after the window, the wave would have already passed them by.

What's important about the latest generation is that they were born right when the PC was becoming available to the masses, in the early 1980s, which meant that many grew up with one in their home.

"That was huge," Bajarin said. "They already knew how a PC works, and in a lot of their cases they had PCs in their homes because their parents had PCs in their homes; whereas the generation before them, the production of digital technology was more of a product in the toy category."

The gender gap persists

However, the PC wasn't marketed to everyone across the board. In 2014, NPR used data from the National Science Foundation, American Bar Association, and American Association of Medical Colleges to show that computing companies stopped marketing their machines to girls around 1984.

It's had dramatic effects on female representation in computer science fields to this day. Women earn 57% of all undergraduate degrees but only 18% of all computer and information science degrees.

Underrepresentation is only the start, though. Sexism and sexual harassment scandals have plagued the industry for decades. Women also have a much harder time earning venture capital money. One study found that even if there was just one woman on a company's executive team, the company tended to receive less funding.

A recent manifesto written by a now ex-Google staffer that criticised the company's emphasis on diversity is only the latest example of how women can be dissuaded from staying in the tech world.

The factors come together

It wasn't all boys who used the first PCs — rather, those from predominantly affluent areas. In 1981, the average PC cost $US1,565, or about $US4,100 in 2016 dollars. And if you wanted to buy the first Macintosh when it came out in 1984, you had to fork over $US2,495, or nearly $US5,700 today.

Sam Altman, the 32-year-old president of Y Combinator, Silicon Valley's largest startup accelerator, said growing up in St. Louis he had a Mac LC II at home, but most of his hacking took place on his elementary school's Mac IIGS. He would spend hours writing simple programs — a luxury kids living in poorer areas, with poorer schools, wouldn't necessarily have.

 "You could write a program to print all the prime numbers, and come back to school the next morning and the computer's run all night, and it's gotten to like to prime number a million-something," he told Business Insider. "And you think it's so cool."

When the dot-com bubble formed in the late 1990s, the kids writing these simple programs were now in their late teens. And since the internet's transformation was on display for all to see, through news media and the internet itself, these teens had a front-row seat, says Paul Saffo, a Stanford consulting professor and technology forecaster. This visibility, Saffo claims, is ultimately what separated the new tech generation from the old.

"During the dot-com bubble, when so many people are starting companies, you say to yourself, 'Well, that's not an aberration,'" which is how many viewed Gates' and Jobs' rise to prominence, he told Business Insider. Instead people said, "That's a career track."

That mixture — years of preparation as a kid combined with a budding tech landscape on the verge of tectonic change — ended up sending a slew of young tech geeks into a field that would write history books.

"The mobile explosion was starting to take off," Tim Bajarin said. "And the opportunity was very large."

The next big thing

Not all of today's most prominent tech founders are in their 30s. Tesla and SpaceX CEO Elon Musk is 46. Amazon CEO Jeff Bezos is 53. Likewise, a number of younger founders born after that early 1980s wave are rising to the top. Evan Spiegel and Bobby Murphy, the cofounders of Snap, are 27 and 29, respectively.

Nor did every founder between 33 and 36 launch their company at the same time. Mark Zuckerberg launched Facebook in his college dorm in 2004, for example, while John Zimmer didn't cofound Lyft until 2012.

More important are the experiences they had growing up, and the relationships they formed to technology at the time. Altman says he grew to have such a fascination with computer programming specifically because he could write simple code that would print out strings of prime numbers. It didn't matter he wasn't creating super-smart apps — the seeds of inspiration were getting planted at the right time, with tech that was sufficiently hackable.

"If you give a kid an iPad today, they will have a great time," Altman said. "But if you want to go make an app for an iPad it's a lot of work. A 7-year-old is not going to figure that out for him- or herself."

According to Saffo, the same wave Gates and Jobs rode and which resurfaced for Zuckerberg and many others is poised to happen a third time in the field of genomics. He said technologies like CRISPR, a gene editing tool, are ripe for innovation in the coming decade.

Altman, however, said to look at whatever the smartest kids in the best universities are talking about, and ignore the hype. "Because everybody says that," he said, "I expect that it's wrong."

This article first appeared on Business Insider. Read it here or follow BusinessInsider Australia on Facebook.